In pipeline systems, to repair a break or leak in a section of the system, or to extend the system by a branch pipeline, it is common practice to secure a T-fitting to the pipe to be repaired or extended by a branch line. The T-fitting having a seat therein in or upon which a plug can be seated to prevent fluid flow through the fitting from the mainline pipe without interrupting flow through the latter. Conversely, it may be desirable to remove the plug from the T-fitting without interrupting flow through the mainline pipe.
Since such systems frequently carry a flow of fluid, such as oil, under high pressure, complicated apparatus is normally required to seal off the T-fitting while the plug is installed or removed to prevent loss of fluid from the system. Such apparatus frequently includes a gate valve, or the equivalent valve, for opening or closing fluid flow through the fitting while the plug is installed or removed by the apparatus. Since such valves are expensive, it is usual practice to remove the valve after a fitting has been plugged to release the valve for service elsewhere, and then to simply cap the fitting with a blind cap.
Such pipeline systems and the repair and extension thereof, T-fittings used therein, gate valves used therein, plugs for plugging the fittings, and apparatus for seating and unseating the plugs in the fittings, are illustrated and described in the brochures of T. D. Williamson, Inc., of Tulsa, Okla., and the patents listed therein, as follows: No. 501.0 (Apr. 15, 1970); No. 502.0 (Apr. 15, 1970); No. 502.1 (Jan. 15, 1968 ); No. 503.0 (Jan. 1, 1965); No. 504.0 (Mar. 1, 1969 ); and No. 505.0 (Mar. 1, 1969).
Many of such pipeline systems in commercial use are employed to carry a fluid, such as oil or refinery liquids, not only at relatively high pressure, e.g., 1000 p.s.i., but at high temperatures of the liquid, e.g. 500.degree. - 700.degree. F. None of the conventional methods or equipment of which I am aware for plugging a T-fitting or branch line in such a pipeline system without interrupting flow in the system are capable of satisfactory operation is such a high-pressure, high-temperature system, and it is a primary object of this invention to provide a T-fitting, a plug therefor, and apparatus for installing and removing the plug without interrupting flow in the system, which can be satisfactorily used in such a high-pressure, high-temperature system.